searching for Crank
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fanofpetty
senior member
68 to 71 340s use a stronger forged crank, the 72 and 73 340s and all 360s used a cast crank. I personally won't build engine with a cast crank.
moparlover
Well-Known Member
i dont think they came out with cast cranks in 340's until 72 or so... better check into that
Dodge33
Well-Known Member
The cast crank 340 motor would have to be a late built 72 model year
or 73 year. The 73 340 motor's were all cast crank motor's as far as I'm aware of. Good luck with your search.
or 73 year. The 73 340 motor's were all cast crank motor's as far as I'm aware of. Good luck with your search.
Why a cast crank versus the stronger forged unit Uli?
PapstXX
Well-Known Member
OK Thx brother and sisters for your information and fast answer 
)))
I have changed me question !
Leanna sorry i have expressed myself wrong :-((((((
We want to drill a 318 to 340 and therefore we need the 340 crankshaft
)))I have changed me question !
Leanna sorry i have expressed myself wrong :-((((((
We want to drill a 318 to 340 and therefore we need the 340 crankshaft
The forged cranks were in all 340 blocks with casting date of 71 and earlier. all cast cranks are in 72 casting dates.
VDART
Well-Known Member
isn't the 318 crank the same as a 340-- stroke wise? so a 318 forged crank is the same as the 340? Lawrence
Engine Years (USA)* Stroke Bore
3.9 1988-2003 3.31 3.91
273 1964-69 3.31 3.63
318 (5.2) 1967-2002 3.31 3.91
340 1968-73 3.31 4.04
360 (5.9) 1971-2002* 3.58 4.00
488 V-10 1991 - 2002 3.88 4.00
505 V-10 2002 - 3.96 4.03
* They put the 360 in a few of the trucks in early 2003. Rovell Rangel
Engine Years (USA)* Stroke Bore
3.9 1988-2003 3.31 3.91
273 1964-69 3.31 3.63
318 (5.2) 1967-2002 3.31 3.91
340 1968-73 3.31 4.04
360 (5.9) 1971-2002* 3.58 4.00
488 V-10 1991 - 2002 3.88 4.00
505 V-10 2002 - 3.96 4.03
* They put the 360 in a few of the trucks in early 2003. Rovell Rangel
fanofpetty
senior member
yes a 318 forged crank is the same as a 340 forged crank and can be used in a 340 block. The eariler 318 poly motors are also forged crank motors and can be interchanged as well.
But the 318's used lighter connecting rods than the 340's.
I thought all "LA" 318's were cast cranks. You could substitute a 273 forged crank for them though. Same main bearing diameter and stroke.
Locomotion
Well-Known Member
Whichever crank is used, it will need to be rebalanced.
* Early 273 cranks had a small converter register so a more common, later model converter with the larger snout will not fit without machining the back of the crank.
* Some earlier 318's had forged cranks. Forged 318 truck cranks use to be favorites because they were stronger. I believe the journals were solid, but i don't recall for sure. I have one with a worn thrust surface somewhere in my garage.
* "We want to drill a 318 to 340 and therefore we need the 340 crankshaft"
If this means boring out an OEM 318 to a 340 bore, then I would not recommend it. 318 cylinder walls would end up too thin for proper ring seal and overall strength.
* Early 273 cranks had a small converter register so a more common, later model converter with the larger snout will not fit without machining the back of the crank.
* Some earlier 318's had forged cranks. Forged 318 truck cranks use to be favorites because they were stronger. I believe the journals were solid, but i don't recall for sure. I have one with a worn thrust surface somewhere in my garage.
* "We want to drill a 318 to 340 and therefore we need the 340 crankshaft"
If this means boring out an OEM 318 to a 340 bore, then I would not recommend it. 318 cylinder walls would end up too thin for proper ring seal and overall strength.
fanofpetty
senior member
138s used both forged and cast cranks depending on vehicle application. trucks generally forged cranks.
fanofpetty
senior member
typo....above 318s
If I understand you're question, You want to make a 318 into a 340 byOK Thx brother and sisters for your information and fast answer
I have changed me question !
Leanna sorry i have expressed myself wrong :-((((((
We want to drill a 318 to 340 and therefore we need the 340 crankshaft
boring,"drilling," it to the 340 size. Can't be done. The cylinder dia. for a 318 is 3.910, and the 340 is 4.040. You'll be into the waterjacket long before you get the 318 bored,"drilled," to the 340 size. The 273, 318, and 340 cranks will physically interchange, but they're all balanced differently
because of the different weights of the pistons etc.
Locomotion
Well-Known Member
Even if you don't get into the water jackets, the cylinder walls will be too thin and will actually flex and not allow a good ring seal. It will not perform to it's full potential and can eventually break. I don't know what the minimum wall thickness is, but you won't have it with a 318 block bored out that much. Sonic checking is the only way to make sure you have a "safe" cylinder wall thickness and any thicker ares should favor the "thrust" side of the cylinders..
If you don't break into the water jackets with the overbore, you may do so with the cylinder sleeves. Some people don't have a problem sleeving a block to restore a damaged bore. But most people will agree that sleeving a block to get a bore bigger than it was designed for is not a good idea. It will reduce the over strength of the block. I believe 318 main caps are also a bit smaller and weaker than on a 340. Same size, but less metal is used.
I'm sure Mopar blocks are very rare in Europe. But you would be better off trying to find a 360 block which might be easier to find than a 340 and has a bore closer to a 340. It has a cast crank, but the main journals are bigger and stronger than a cast 318/340 crank. A 360 can make and handle a lot of HP, as long as you don't get carried away with the HP goals and rpm's.
swinger340
Well-Known Member
I have seen and pulled apart a 72 340 out of a stick car that had a forged crank. Surprised the hell out of me. Then again I guess someone could have been in the motor prior to me.
lead69
hopeless car junkie
Some early 72 340s had them,also the forged 318 cranks do have solid jornals like loco stated.
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